A San Francisco man who was found slain in the Mission District last month apparently was strangled, police said Thursday.

Richard Sprague, 47, was found the morning of Feb. 19 on the sidewalk on the 100 block of Julian Avenue, between Mission and Valencia streets near 15th Street. Preliminary investigations by the medical examiner and the police homicide unit suggest he was strangled, said Officer Albie Esparza, a police spokesman.

Sprague left to buy cigarettes early that Sunday morning and never came back, said David Nielsen, his domestic partner.

"He was trying to quit," Nielsen said. "I didn't take him because I don't want to enable the whole cigarette thing. And then he walked out of the house, and I never saw him again."

Sprague and Nielsen, 59, lived in an apartment several blocks from where Sprague was found. The couple moved there around 2004 and had been together for almost 20 years, Nielsen said.

Sprague left with cash to buy cigarettes sometime after midnight, but didn't take his wallet or cell phone, Nielsen said.

Police posted a flyer in the neighborhood after the slaying that said Sprague was robbed and killed between 2 and 3 a.m. The first call for a well-being check on the body came around 7:30 a.m., police said.

"He did not deserve to die that way," Nielsen said.

No arrests have been made.

Sprague was a certified gemologist who worked in the jewelry department at the downtown Neiman Marcus until 2009, when he had to quit because of an accident the year before that made it difficult for him to walk without pain, Nielsen said.

Sprague was an animal lover who had several rescue dogs, said Debra Lunardini, a former colleague at Neiman Marcus.

"I was initially very, very angry" about the killing, Lunardini said. "But Richard wouldn't want us to be angry. He was that big a guy."